OHS Code Explanation Guide

Published Date: July 01, 2009
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Part 41 Work Requiring Rope Access

Section 842 and Section 843 Fall factor, clearance, anchorage strength

Forces are created primarily by a falling climber and, while lead climbers generate the greatest forces, second falls can also produce significant loads. Since measuring the actual load is a complex process affected by many variable, means for measuring the relative severity of a fall rather than actual loads or force have been devised. Fall Factor (FF) describes the relative severity of a fall.

Fall factor is a relationship between the forces generated in a fall and the shock absorbing qualities of the rope. Since climbing ropes are highly elastic they absorb tremendous amounts of energy as they stretch under load. Fall factor takes this stretch into account when calculating the severity of a fall. Fall factor is expressed as the relationship between the total length of a fall divided by the amount of rope available to absorb the energy.

Fall factor = length of fall/length of rope in service

Referring to EN Standard 892 and UIAA Standard 101 for dynamic ropes (see the explanation to section 818 for more information about these standards), the peak forces generated in the rope cannot exceed:

  • 12 kN in single ropes (single strand of rope)
  • 8 kN in half ropes (single strand of rope)
  • 12 kN in twin ropes (double strand of rope)

These values are achieved with a rigid test apparatus. In real life situations, the rope system experiences slack and some degree of slippage and movement.

The dynamics of non-industrial rope access work and how an anchorage point may be used are far different from a worker using an anchor point for fall arrest. The anchor point(s) are under a constant and varying load depending upon the rope access technique being used. The maximum arresting force generated in a rope access environment can depend on many variables including, but not limited to, the length of rope in service, slack in the rope system, mass of the worker, type(s) of devices being used, slippage and movement of the rope in the system, and how secure the anchorage is against movement under load and the extent to which it might deform without failure. Combined, these factors make it extremely unlikely that the peak forces listed above would ever be experienced. A fall factor of 1.78 would, with the exception of lead falls, rarely be experienced.